Composite (CaF2 + α-Al2O3) solid electrolytes: Preparation, properties and application to the solid oxide galvanic cells

Abstract Calcium fluoride based composites containing up to 25 mol. % α-Al 2 O 3 disperse phase were prepared. Electrical conductivities of the samples were measured in the temperature range 400–700 °C by the d.c. four-probe method. Dispersions of α-Al 2 O 3 up to 5 m/o were found to enhance the conductivity of pure CaF 2 . The conductivity values were increased two orders of magnitude higher than those of pure CaF 2 and they were dependent on the preparation method of the sample. The maximum conductivity values were observed for 2.5 m/o α-Al 2 O 3 content. The (CaF 2 + α-Al 2 O 3 ) composites appeared to be purely ionic conductors. The materials prepared were applied as electrolytes in solid-state oxide galvanic cells. The Gibbs free energy of formation at 700 °C for calcium metasilicate was determined from electromotive force (emf) measurements in this way.